[gnome-calculator] snap: Updated for core18

[Ken VanDine <kvandine src gnome org>]

commit bc1282b5013584cebd986933d63c694684857f8d
Author: Ken VanDine <ken vandine canonical com>
Date:   Fri Mar 8 11:50:52 2019 -0500

    snap: Updated for core18

 snap/snapcraft.yaml | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)
---
diff --git a/snap/snapcraft.yaml b/snap/snapcraft.yaml
index 77513995..dc349091 100644
--- a/snap/snapcraft.yaml
+++ b/snap/snapcraft.yaml
@@ -22,12 +22,13 @@ description: |
 
 grade: stable # must be 'stable' to release into candidate/stable channels
 confinement: strict
+base: core18
 
 plugs:
-  gnome-3-26-1604:
+  gnome-3-28-1804:
     interface: content
     target: $SNAP/gnome-platform
-    default-provider: gnome-3-26-1604
+    default-provider: gnome-3-28-1804
   gtk-3-themes:
     interface: content
     target: $SNAP/data-dir/themes
@@ -63,6 +64,17 @@ apps:
       LD_LIBRARY_PATH: $LD_LIBRARY_PATH:$SNAP/lib/gnome-calculator
 
 parts:
+  desktop-gnome-platform:
+    source: https://github.com/ubuntu/snapcraft-desktop-helpers.git
+    source-subdir: gtk
+    plugin: make
+    make-parameters: ["FLAVOR=gtk3"]
+    build-packages:
+      - build-essential
+      - libgtk-3-dev
+    override-build: |
+      snapcraftctl build
+      mkdir -pv $SNAPCRAFT_PART_INSTALL/gnome-platform
   gtksourceview:
     after: [desktop-gnome-platform]
     source: https://gitlab.gnome.org/GNOME/gtksourceview.git